Control apparatus for heating plants



Aug. 26, 1952 T. H. LANDGRAF El AL CONTROL APPARATUS FOR HEATING PLANTS Filed May l1, 1950 M f /Zl Patented Aug. 26, 1952 CONTROL APPARATUS FOR HEATING PLANTS Theodore H. Landgraf, Aurora, and Francis A. Furlong, Chicago, Ill., assignors to Autogas Company, Chicago, Ill., a company Application May 11, 1950, Serial No. 161,428

This invention relates to control apparatus for p heating plants and more particularly to apparatus for controlling a space heating furnace employing a fiuid fuel.

, In space heating the optimum type of 'control would be one in which exactly the right amount of heat is supplied to the space under all external conditions exactly to balance the heat losses, thereby to maintain the space at exactly uniform temperature at all times. This exact type of control is impractical, especially for domestic heating, since it would be far too complicated and expensive. It is desirable, however, to approach the optimum as closely as practical limits will permit.

One arrangement which has been used successfully is disclosed and claimed in the patent to Furlong No. 2,164,511. In this arrangement two preset rates of fuel supply are provided and one or the other is selected depending on the demand as measured by a thermostat. In this system the heating plant is started with high input when a predetermined low temperature is reached and changes to low input as the temperature rises and finally is shut off when the temperature reaches a predetermined higher value. The present invention has for one of its objects to provide certain improvements in this system to maintain a more uniform temperature under extremely mild conditions and to insure high input immediately in the event of a rapid temperature` drop.

f Another object is to provide a control apparatus' in which low input will be provided as soon as a predetermined high temperature is reached and will be maintained until the temperature rises above said high temperature or drops below a predetermined lower temperature. `According to one feature of the invention, a time lag snap acting control is provided to control starting and shut `o`ito insure a minimum period of operation eachtime the predetermined high temperature is reached. According to another feature, provisions are made to insure immediate starting at high input any time the temperature falls below the predetermined lower temperature.

The above and other objects and features of theinvention will be more readily apparent from the following description when read in connection with the accompanying drawing, in which:

Figure 1 `is a .diagrammatic view Vwith parts shown in section througha fuel conduit and control valve to which the control apparatus of the present invention is applied,vFigure 2 is a circuit diagram of the control apparatus of the inven- 7 Claims. (Cl. 236-1) tion, and Figure 3 is a partial sectional view` illustrating a modified construction.

As shown in Figure 1, fluid fuel such as `gas is supplied to a heating furnace througha mainl supply conduit I I from any suitable source. "A main valve I2 `is provided in the conduit Vcon-Q trolled by an electric ymotor I3 which opens thej valve I2 whenenergized andallows Athe valve to close under the influence of aspring or? the like when the motor is' de-energized. This type of motor is a standard commercial unit and will not be described herein in detail. When the valve is open,v fuel will be supplied to the furnace' and when it is closed the'supply of fuel will` be( interrupted, except that ordinarily a pilot burner is provided supplied through a bypass around thev valve I2 for automatically igniting the main burner when the valve 'I2 isope'ned. i A

In addition to the main valve I2, a secondary control valve I4 is provided in the conduit II. A bypass I5 4is provided around the valve and an additional adjustable bypass I6 mayvbeprovided to adjust 'the amount of fuel which will flow` past the valve I 4 when it is closed,V The valve I4 corresponds to the similar modulating 'valve more particularly `described and claimed in Patent No. 2,164,511 and, as shown, is urged open by a spring I'I and is closed by a diaphragm I8' when pressure is supplied to the lower sidel of the diaphragm. A small bleed passage @extends from the space below the' diaphragm I8 tothe furnace side of the valve I4 to prevent trappingl of actuating fluid beneath thediaphragm.

The motor I3 is controlled by Va room thermostat 2l having a pair of blades 22 and 23 to engage fixed contacts 24 and 25 at different temperatures'. 'I'he thermostat is connected in a control circuitto the motor I3 and to a control' apparatusfindil cated generally at 26, to control the supply of actuating fiuid to the diaphragm I8. APreferably the fuel supplied to the furnace is utilized a'sthe` actuating iiuid, and for this purpose the main conduit II is connected through a pip'eZ'I to the control mechanism 26, which is in turn'connected through a pipe 28 to the space below the diaphragm I8. When fuel flows through the pipes 21 and 28, the diaphragm I8 will be subjectedto pressure to close the valve I4, while when there is no flow through these pipes, the pressure will bleed off through the opening I9 to allow the valve I 4 to open. The control circuits preferably go through a pilot operated switch 29, which is shown as a mercury switch tilted through a pilot control thermostat .by means of a link 3l so that the main valve cannot be opened except vwvlien the pilot is burning.

in response to a limit control on the furnace toV be normally closed but to open whenthefurnace exceeds a predetermined temperature. The limit-V control switch circuit is also connected to a contact 42 adapted to be engagedjbyv ai contact 43 carried by a bimetal strip. 44lwhen the.strip.` 44 is heated. The strip 44 is connecteditoawter-L. minal 45 on the motor Whichleads toA one. side of the motor I3 and also to one terminal of a holding switch 46 actuated by the motor throughv a cam 41. The other side of the motor is con nected to a terminal'48f,` which is inturncon'fV nected to the suppl-yterminal 33:

TheY bimetal strip- 44 is heated by aresistance heater element' 491-connected; at `onesideto the terminal. 45 `and f at its other side to.V the common orV center terminal f of -the thermostat. Accord--V ing-` to one feature of f the invention-thefs'witch` 43.- isl adapted-to remainclosed for a-predeter-` minedperiodof. time oncefit` is closed. lorithispurpose-the contac'e43vis4 formed by=k a disc oir magneticmaterial and` ay small magnet 5lis mounted adiacent-tothecontact4-2i When the strip 44 is'heatedsuiiiciently tomoveethe: contact-43 almost intoiengagement4 with the con-. tac-t 42. thevmagnet 4i-will deectthef strip bring the-'contacts firmly v into engagement,l with'` no"chatteringni` Ast thebimetal strip cools andA tends to move the contact 43^awav^from-the .cone tactY 42, the magnet 5|- willholdthev strip deected with the contacts.. in engagement. until. it' reachesf atemperature lower than that` at which'ithe contacts initially engage andwillzthen. release the contact 43. so.` that it will spring. cleanly awayy from` the contactA-z with.y a.. snan.

action. This construction. therefore, provides for snapY actionengagement and disengagement..

and insures that the circuit throughthese contacts will remain closed for.- a. predeterminedminimnmtime interval. The center contactv ci the thermostat is also connected tothe holding switch' 43, asshow-n; whichl isin parallel with a theheater 49 -sothat when the holding switch.

is closed; no currentgwillowfthrough the heater. and it will cool ofi". l

To open the valve I4v for highfuel supply, theV control mechanism: isi:nrovidefl.v which. may beconstructed as' best Yseenin Figure 2; shown. the pipe 21-ex-tends`into a c-lnsedhnusing to which thepi'oe Pris connected and..terminatesv in a nozzle portion adam-ted to be. engaged bv. a apner- 52; Theanper 53 isnivot-ally. mounted Onal bracket 53iandfis normally urgedf'awayfrom. the nozzlebv aspring 54. In'thisvcondition the nozzle will bel onen so that(l gas ork other fuel under' pressure can'ow through the control unit' to' raise the diaphragm I8 andclose the valve I4.

`To close the nozzle a solenoid 55 is provided t; attract the apper t2 and seat it' against the nozzle.v One side ofthe solenoid is connected to a terminal 55,.which is connectedv to the contact.25 ofthethermostat. The other side of the solenoid is connectedthrough a resistance l to the supply terminal 3,3 and also through a resistancef 58 to the terminal 45. Preferably the terminal 56 is connected. through the resistancey Aslv '4 58 to the terminal 45 as shown, for a purpose to appear more fully hereinafter.

In operation of the system, when the temperature is above the maximum limit for which the thermostat is set, say, for example, 72, both thermostat contacts will be open and the motor will beide-energized so that theyvalveIZ is closed and no fuel is supplied tothe furnace. When the temperature drops to the upper setting limit, the blade 22 will engage the contact 24 to complete a circuit from the power terminal 34 to terminal through the switches 23 and 4I to the thermostat contact 24 and blade 22 and through-the heaterlltto the terminal 45. This circuityiscompletedthrough the motor to the terminal 48; and the power input terminal 33, but the resistance of the heater 49 is such that the motorv will not operate. As the heater heats theblade44, the contact 42 will engage the contact 43 to complete a circuit from the limit switch Y 4I .parallel tothe circuit through the thermostat mainathigh input-raslong.-asthecontact23 is.,

tothe. terminal 45; Since this is aplow resistance` circuit, themotor will be energized to'opentlie valve I2 and initiate the supply of fuel tothe furnace.

As soon as theymotor turnsJ the cam -41 will closethe holding switch 45to complete aholding circuit. parallel to the last described circuit fromtheterminal 35 through the switches Zland 4I,

through the thermostatl andswitchv4tl to the terlfilllal.Y45.` This is also a4 low resistance circuit' and, supplies enoughgcurrentto the'motor to main'- tainit in its energized position with the*` valve I2. open. It. is, noted thatA this circuitjincludes the thermostat contact 24 and blade22 softhat' the motorwillbe,energized only as longvr as'these thermostat contacts.. areY closed. or" while the Switch 42,n 43 paralleL therewith is closed.; Therefore.. after. arrinterval sucient for the.

switch bladel 431th move outof engagement `with the. contact 4.2themotgr circuit will be inter'-` rupted. to closethe valve I2. wheneverthe temblade 22,- is set.v

Upon a, further l decrease.. in;L temperature, forU example, to 'lothethermostat blade23 will en thediaphragm., I twillbedissipated andlth valve I4.will.be open. i This increaseslowof intl. t9 theY fiurnacerto high. input-andthe furnace will ref in engagement withrthe lthermostat terminal, 2,5.Y

As soon' as thisl contact: isrbroken. upon a risesY in temperature, the solenoid 5 5 vwill be: die-ener-` gized, allo-wing' the valve 52 to :open so tl'iat-"thevalve I4 will bev closed and the furnace.willre.

turn to its' low inputl condition. vThus-the fur-V nace is normally started at low input and reg-- mains onlow input as long as the temperature is below thatv for. which thermostat, blade 22 is set;

and above` that .for which blade 23 isset. In

extremely mild weather, the blade V23. will V norr. mally never c11oseso that the furnacecycles quired to maintainthe.predeterminedminimum temperature..

Upon aY sudden dran/in.. temperature, such. asV4 This connects the heater 49 and resistor` 58 'par-` allel and their parallel resistance isr low enough torperrnit operating current .to iiow `through the motor I3 to open the valve I2. -At-thev same time the solenoid 55is energized to close the pipe 2l so that the valve I4 will open fonhighinput. It isnoted that the furnace is started under` these conditions without waiting for heatingrof the blade ,44 andfstarts at high input; other normal operating-conditions the furnace starts under lowfinput and Vremains at low` inputllrntil the temperature has dropped sufficiently toclose the blade 23. Y l

Figure 3 illustrates an alternative construction `of thegcontrol'valve unit `for controlling supply of fuel .undenpressure' to the diaphragm I8. As shown, fuel normally flows from the supply conduit ahead of the valves through a passage @Land ilowsout through apassage 32 to the diaphragm I8. The passage'IZ may be closed by a plunger 613 which is normally urged upward by a spring E54 to leave the passage open. The plungeryS is moved down by a bimetal strip 55, heatedby aresistance `heater 66, whichrnay be connectedin the circuit in place of the solenoid 55p` In this circuit the Aresistance 51 may `be omitted; since its place is taken by the heater 65 and the right side of the heater may be connected directly tothe terminal 45 rather than through the resistance 58 as shown. Otherwise this construction functions in the same manner as that of Figures 1 and 2. l

While two embodiments of the invention have been shown and described in detail, it will be understood that they are illustrative only and are not to be taken as a denition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

1. Control apparatus for a heating plant using liuid fuel and having a main on-off valve controlling the supply of fuel comprising an auxiliary fuel control device controlling the supply of fuel and having a normal low position in which a relatively small quantity of fuel is supplied and a high position in which a greater quantity of fuel is supplied, a thermostat responsive to the temperature of the space to be heated, means in the auxiliary device normally to bias it to its low position, a i'lrst circuit closed by the thermostat at a predetermined temperature, means operh ated by the first circuit to open the main valve without affecting the auxiliary device, a second circuit closed by the thermostat at a lower temperature to adjust the auxiliary device to its high position, and a third circuit closed by the thermostat at said lower temperature to open the main valve independently of the operation of the said last named means.

2. Control apparatus for a heating plant using fluid fuel and having a main on-oif valve controlling the supply of fuel comprising an auxiliary fuel control device controlling the supply of fuel and having a normal low position in which a relatively small quantity of fuel is supplied and a Under `all` accanita l l l e" high position in which is supplied, a thermostat responsive to the temperature of the space to be heated, a switch to control the main valve, time delay means energized by the thermostat at a predetermined tem-` perature to operate the switch to open the main valve, means operated by the main valve to hold it open as long as the thermostat is below said predetermined temperature and to deenergize the time delay means, and means operated bythe thermostat at a lower` temperature to control the ature of the Space to be heated, a switch to control the `main valve, time delay means energized by the thermostat at a predetermined temperature to operate the switch to open the main valve, means operated by the main valve to hold it open as long as Athe thermostat is below said predetermined temperature, a circuit closed by the-thermostat at a lower predetermined temperature to control the auxiliary device, and a second circuit closed, by the thermostat at said lower temperature to open the main` valve indepenclentlyof` said switch.

4. Control apparatusl fora heating plant using fluid fuel and having a main on-off valve con- 4 trolling the supply `of fuel comprising an auxiliary lfuelv control device controlling the supply of fuel and having a normal low position in whichl a relatively small quantity of fuel is supplied and a high position in which a greater quantity of fuel is supplied, a thermostat responsive to the temperature of the space to be heated, a switch to control the main valve including a bimetallic strip which closes the switch when heated, a heater circuit for the strip energized by the thermostat when it is below a predetermined temperature, magnetic means tending to hold the switch closed, the switch and heater circuit being in parallel circuits including the main valve, a holding switch closed by the main valve when it is open and in series with the thermostat to hold the main valve open when the thermostat is below said predetermined temperature, and means operated by the switch at a lower temperature to control the auxiliary device.

5. Control apparatus for a heating plant using fluid fuel and having a main on-oif valve controlling the supply of fuel comprising an auxiliary fuel control device controlling the supply of fuel and having a normal low position in which a relatively small quantity of fuel is supplied and a high position on which a greater quantity of fuel is supplied, a thermostat responsive to the temperature of the space to be heated, a switch to control the main valve including a bimetallic strip which closes the switch when heated, a heater circuit for the strip energized by the thermostat when it is below a predetermined temperature, magnetic means tending to hold the switch closed, the switch and heater circuit being in parallel circuits including the main valve, a holding switch closed by the main valve when it is open and in series with the thermostat toV hold the main valve open when the switch is closed or the thermostat is below said predetermined temperature, the heater circuit' having a,

a'greater. quantity of fuel high. resstancewsuch that thecurrentthrough h l ill be Vin'suic'z'ient' tcoperateit w no ly the'heater'circuit is closed, andfa 'oi'r" 'in 'parallel 'te the'lhe'ater 'circuit closed` by the Y*tlflerrnest at 'at a lower 'predetermined' tomA valv peratuefandieduoing the' resistance in circuit with'th mai/ rl valve toT the point' wherewthe'rnain' valve will' beo'peratea '962v Control apparatus foraheating plant using.

trollingthe supply of lfuel vcor'npris'ing an all-l iliary Vfuel'controldevice controlling thejs'upply of fuel `anolhavinga normal loW, position in which alrelatively'shiall quantity of fuel issupplied and. afhighz'vposition, in which a greater quar'itity of.; tue islsiippld, av thermostat responsive 'tothe'. ternperature ofthe space tobe heated, the their'v mostat having a, high 'contact toclose'at a predeff'jr ter'minedtemperature and a low contact to close@ ataY predetermined lower ternperaiure,v acircfuit between the high' 'Contact 'and the main valve 111-" cludingvea resistance unit of sufficiently high re-l sistanceto prevent Yoperationfof 'the main`v'alve whenl' only 's'aiclv circuit i's energized, 'ajswit'ch in` shuntrwi'tn the resistance unit'to establish' a' tactto operatek the auxiliary device.

'1."Controlapparatus'for a heating plant using fluid fuel andv having a main on-oifV Valve con;A

trolling the supply of fuel comprising an aux'- iliaryfuel control cletic'ey controlling 'the supply of [hai/ing anormal low `position incwhich a relatively small quantity of fuel, is suppliedand` mostatf'haiiingla'high lcontact to' close'y at aprecie'-v terminenv 'temperature 'andA a low contactto close at "a predetermined lower temperature; a Vcircuit' between the high Contact and the-main vaiveing' oludingca resistance unit of sufficiently high ref-j sista'rlce to prevent operation'of themainwalve' when only "saidv cicuit'is energized, a' switchjin' shurritwith the resistance Vunitto establish a main" valveoperating v circuit, time "delay" means operi ated, bythe 4'resistance 'unit' 'when' it is` energized'v torblose the switch; a "holding 'switchQclsed 'by' the opening'rof'thefmain'valve' 'anti in circuit'with the high" contact to"lfio1d' 7the""nain"valve' operi' when either' the high Contact" r'the' switch 'i'sclosed, acicuit controlle'dbyclosin'g offthelow"Av Vcontaxbtfto adjustthe'auxiliary dviceto rits lhigh position', and 'another circuit `controlled by closf `verve win be pperated.'

ing of the low Contactin'parallel'-with'sad'f sistance `unit toreduce therresist'ance' in circuit; with the main valve to the point 'where theinain" 'I'HEODORE H. LANDGRAF. FRANQISAJEURLQNQ Y REFERENCES CITED The 4followiri references are 'ofn recorly theY le oi` this l patent UNITED' STATES.. RArENTs Number Name Date 2,184,982 'lorz'iquist"- Dec."'26;"1939 2,329,636V McGrath" Sept. 1'4', 1943' 2,355; 436 Hayter l; Aug'. 8,' 1944'Y 2,461,608" Laingr` l'eb. 15, 194Q9 

